The present invention relates generally to a method and apparatus for separating solid particulate materials to recover a desired particulate material from a mixture of contaminated media containing the desired particulate material. More specifically, the present invention relates to a compensating flow control assembly used to automatically adjust the amount of contaminated media flowing through a magnetic separator or an air wash separator to be cleaned and reused in other equipment.
Shot blast media such as that used to surface finish or clean castings, forgings, and other such items are propelled by shot blast equipment at the workpieces at very high velocity. As a result, the blast media gradually breaks down into fine dust-like particles called “fines” which are no longer efficient as abrasive media. In addition, the action of surface finishing or cleaning of workpieces such as castings and forgings results in metallic debris such as scale and rust, and non-metallic debris such as molding sand becoming intermixed with and thus contaminating the abrasive shot blast media. Thus, contaminated shot blast media is typically a mixture of re-usable metallic shot, broken down shot (the “fines”), metallic debris, and non-metallic debris. Magnetic separators and air wash separators are well known in this art, and are particularly adapted to separate and recover metallic shot blast media for reuse in shot blast equipment from mixtures thereof with undesirable contaminants.
A typical magnetic separator has a rotary screen drum for receiving contaminated shot blast media, and a rotary magnetic drum positioned below the screen drum for separating the metallic shot blast media from the other contaminants. An air wash separator is similar in that it typically utilizes a rotary screen drum to receive the contaminated shot blast media, but instead of a magnetic drum air wash systems utilize blasts of air forced across the contaminated media to separate the desired shot blast media from other contaminants. A spill gate assembly is positioned between the rotary screen drum and the rotary magnetic drum, or the air wash chamber, to control the flow of the contaminated shot blast media to the rotary magnetic drum or air wash chamber, respectively. Several key factors are critical to the efficient performance of the magnetic separator, namely, (1) the provision of the thinnest possible thickness or curtain of contaminated shot blast media on the surface of the magnetic drum to improve separation efficiency; (2) the provision of a uniform thickness or curtain of contaminated shot blast media on the surface of the magnetic drum which results in a consistent and balanced composition for the recovered shot blast media; (3) the provision of a full width curtain of contaminated shot blast media across the entire axial length of the magnetic drum to improve separation efficiency and provide a more consistent and balance distribution of recovered shot blast media. Such key factors are also critical for air wash systems.